More Barnes 275 XPB

[Hoot]

How is the weather looking this weekend Hoot?

Good enough to get some range time in?

B.

And well you should ask. The NWS is predicting some payback. Just in time for the Fishing Opener to boot, though my thoughts will be elsewhere. When I was younger, single and had a life, my roommates and I would jump in my boat and go wet a line at every opportunity. Those are all gone now....

I have 10 different load graduations to test across two powders. Only 3-shot runs each, but I need to stretch these babies out. Their numbers are finite. Should be able to harvest something useful from the effort. I did use my last results to calibrate QL and it will be interesting to see if it now tracks linearly upward from where it was calibrated, which in the case of the two slower powders, was mild.

Hoot

[kottke_35]

I've got quite a weekend ahead so unfortunately no load testing for me.

These babies sure a finite, at a buck a piece they ought to put themselves though the same hole!

B.

[Texas Sheepdawg]

I've got quite a weekend ahead so unfortunately no load testing for me.

These babies sure a finite, at a buck a piece they ought to put themselves though the same hole!

B.

And field dress and skin and quarter...PLUS load the critter in the back of your truck to boot!

[Hoot]

Well, It was a beautiful day in the Hundred Acre Woods and I continued where I left off earlier in this thread with less than expected results. That is, at least with the AA1680. I compensated the W296 up about 10% at the starting point since it ran a lot slower than predicted in the first part. That was not the source of my consternation though. I used the same brass as the first part after re-processing it, same primers, same COL, same degree of Taper Crimp, etc.

As soon as I seated the first bullet in the run, I knew something was different by the feel of the seating resistance. These bullets were from newly opened boxes of 275 XPB's and I immediately measured some with the Micrometer. They has an odd shaped in that they were not the same diameter all along the bearing surface. At the heal, they averaged .4511to .4513, but starting around .1 inch above the heal, they got narrower, averaging .4503 to .4508 the remainder of the distance to the ogive. What I felt when seating them was the same relative resistance I recall from from the first part and then the resistance went down considerably until they were full seated. It did not instill me with confidence, but they all did it, so I went to war with the army I had. I did taper crimp them down the same as the first batch, but the results with the slower AA1680 were all over the place in velocity and grouping. So much so, that I indicated which ones belonged to which group in the target images, just so it didn't get hard to follow. The faster W296 was not as adversely affected as the AA1680 and results were relatively consistent, though the POI was still a bit odd.

Here's the skinny:



Yielding 100 yard groups I'm not overly proud of, knowing how well they run with Lil Gun:

AA1680


And

W296


Because I believe in trying new and good ideas, I will be implementing some form of what I will refer to from here on as the "TightNeck" sizing idea proffered by LlindeX Here in tbirdman74's thread about the Taper Crimp. It's a great idea and I added some metrics and visuals supporting my approach to implementing it on page 2 of that thread. In testing my approach, the perceived neck tension was strong and consistent the entire seating length. While this is an attempt to garner better performance consistency in using the slower burning AA1680, I sincerely believe LlindeX is onto something of a paradigm shift WRT how we can best crimp for consistency, aside from using a stab crimp. It may well wind up enhancing velocity consistency and milking every bit of velocity possible for a given charge of all but the fastest powders used to reload the 450B, from any bullet. Especially ones that are narrower than .452. Then again, it may wind up being a dead end street, but it is one I feel compelled to investigate.

More to come...

Hoot

[Hoot]

Shortly after writing the previous post, the mailman delivered two more boxes of the 275 XPBs from my "Secret Santa" and today is yet another Blue Jay Pretty Day. It is also Mother's Day and in the interest of domestic tranquility, I will be paying homage to the better half, at least for a better part of the day starting in a couple of hours. If I fidget and act distracted enough, I may get a pardon later in the day and run to the range to do a short run of TightNecks, which I spent the morning writing a How-To article for others to follow if they need help implementing it themselves Here.

Hoot

EDIT: In measuring a few of the new bullets, they are very close to the ones I used from last year. They run .4513 at the heal and again narrow up above the heal to .4507. Both dimensions are greater than the bore inside diameter, so I have no causative factor to associate why this recently run test went so bad with AA1680 as opposed to the initial run a few weeks ago. Just a bad outing.

[Hoot]

Okay, so much for the paradigm shift WRT AA1680. I am officially declaring that is is a bad choice for the 275 XPB unless you super glue the bullets in. It's just too darn slow and besides, you'll run out of case capacity before getting into the velocity sweet zone.

However, lots of results with W296, that is slightly slower than Lil Gun.

I performed three iterations in this experiment. Some more extensive than others due to conserving my bullets. I want to emphasize that these 3-shot groups are not my method of choice, but until I find the right recipe, they do provide adequate data to make that determination and afford a limited glimpse into what to expect.

In this experiment I loaded up a series of powder steps approaching maximum case capacity using three different crimp options. I did a couple of runs with AA1680 before throwing the towel in, due to no improvement from the last part. The Lion's share of the work was with W296. I've already seen that Lil Gun will works with them, albeit probably a tad fast for the bullet weight.

1) Seat bullets utilizing only the TightNeck approach without a followup Taper crimp.
2) Seat bullets using a combination of the TightNeck and Hard Taper Crimp (.474)
3) One run using a shorter COL of 2.20 inches which allows driving the Taper Crimp into one of the driving band grooves.

Here's the results:



Yielding these 100 yard groups (note: 1/2 inch grid)

TightNeck Only


Tightneck + .474 (Heavy) Taper Crimp


Tightneck With a COL of 2.20 versus 2.26 to allow driving the (Heavy) Taper crimp into the groove


The Tightneck alone, while yielding similar velocities to the TightNeck+ Taper, yielded slightly looser groups. The TightNeck+ Taper yielded some excellent 100 yard groups, when I was doing my job. It was frustrating to throw 2-shots into less than a half inch, only to have a flyer ruin the total group. Admittedly, these are only one-time, 3-shot groups. All were however shot round robin to randomize any hot streaks. That equates to re-positioning the bag and rest every shot, which is distracting and a challenge to overall consistency. It is however how I do it.

Interesting Observations:

The TightNeck+ Taper Crimp seem to be synergistic to accuracy, though less so to velocity.

They didn't help one bit with the AA1680. As I said, I don't think AA1680 could ever be considered appropriate for this particular weight bullet, but I had to try.

If you look closely, you'll see that best velocity for the 41gr charge went to the shorter COL load that allowed the taper crimp to bite into the driving band groove. In my book, that equates to the greatest bullet retention of the three methods I tried. Not necessarily all that accurate though.

All in all a fun outing. Though the wind was gusting in the 20mph range occasionally from my front left, at 100 yards, I did not feel I could blame my occasional group flyer on it. These are heavy bullets and that's not very far. Typical TOF was probably in the range of .15 seconds, so the wind didn't have much time to act adversely upon them.. You could not hear the impact sound which was masked in the persistence of the muzzle report sound.

The jury is still out on whether the TightNeck benefit is worth the extra loading bench effort. It is definitely worth giving a try with lighter bullets where neck tension is more critical than heavier bullets. Just because they get moving faster by virtue of their lighter weight. That will be my next TightNeck experiment.

Yawn. Way past my bedtime after a busy day, which I got off due to having to work a double tomorrow.

Hoot

[LlindeX]

Hoot,

I'm really enthralled with those "Tightneck + .474 Taper Crimp" loads you shot in the above testing! I have not used a taper crimp that tight. I was under the mistaken impression that .475 taper crimp was as tight as we could go without causing headspace problems. The consistency you're getting so far with that combo bears more investigation. Great Job! Thanks for the info.

[Hoot]

Hoot,

I'm really enthralled with those "Tightneck + .474 Taper Crimp" loads you shot in the above testing! I have not used a taper crimp that tight. I was under the mistaken impression that .475 taper crimp was as tight as we could go without causing headspace problems. The consistency you're getting so far with that combo bears more investigation. Great Job! Thanks for the info.

Not at all. While .476 is probably the spec for the case, the die will allow you to take it down way below that. Once, out of curiosity, I took a dummy case with an old, pulled bullet seated in it, down to .460 at the mouth and it still achieved an authoritative, solid "thunk". I only stopped there due to the visible injury caused to the bullet. It's that concern over distorting the bullet too much, that makes me stop at .474. However, it appears that if you're driving the case mouth into the flat side of an all copper bullet like these Barnes, which is harder than a jacketed cup-and-core bullet, it may actually cause the case wall at the mouth to squeeze thinner than it should be, for a distance of .05 to .08 inches, where the most compression is occurring.

WRT the headspace. I've never been comfortable with it since the cases can shrink as much as 20 thousandths after the first firing. I've had new brass start out at exactly 1.700 and shrink to 1.680 after one firing. Look at the difference between a Go and No-Go gauge set. Thank goodness the extractor holds onto the case as strongly as it does.

Hoot

[commander faschisto]

Hoot, thanks for all the 275gr info...you da man!!

[LlindeX]

Hoot,

In your photos of the test load groups, it appears that I'm seeing a sort of scalloping around the edges of the shots on the targets. Is that true? Are the petals on those Barnes bullets beginning to open up before they hit the target? What type of backing was under the paper of the targets? Would it possibly be that they are opening that quickly as they hit the target?